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Orange-hued giant star in the constellation Sagittarius
τ Sagittarii
Location of τ Sagittarii (circled)
Observation data
Epoch
J2000.0
Equinox
J2000.0
Constellation
Sagittarius
Right ascension
19h 06m 56.40897s
[1]
Declination
–27° 40′ 13.5189″
[1]
Apparent magnitude (V)
+3.326
[2]
Characteristics
Spectral type
K1 III
[3]
U−B
color index
+1.185
[2]
B−V
color index
+1.170
[2]
Astrometry
Radial velocity (Rv ) +45.4
[4] km/s
Proper motion (μ)
RA: –50.61
[1]
mas /
yr
Dec.: -249.80
[1]
mas /
yr
Parallax (π) 28.3195 ± 0.3134
mas
[5]
Distance 115 ± 1
ly (35.3 ± 0.4
pc )
Absolute magnitude (MV ) 0.48
[6]
Details
[7]
Mass 1.25
M ☉
Radius 15.71
R ☉
Luminosity 87.6
L ☉
Surface gravity (log g ) 2.15
cgs
Temperature 4,459
K
Metallicity [Fe/H]–0.27
dex
Rotational velocity (v sin i ) 1.04
[8] km/s
Age 7.91
Gyr
Other designations Namalsadirah 2, Rabi al Sadira, τ Sagittarii, τ Sgr, Tau Sgr, 40 Sagittarii,
CPD −27°6617,
FK5 1496,
GC 26291,
HD 177716,
HIP 93864,
HR 7234,
PPM 269078,
SAO 187683
Database references
SIMBAD
data
Tau Sagittarii (Tau Sgr , τ Sagittarii , τ Sgr ) is a
star in the southern
zodiac
constellation of
Sagittarius .
Description
With an
apparent visual magnitude of +3.3,
[2] this is one of the brighter members of the constellation. The distance of this star from Earth is roughly 122
light-years (37
parsecs ), based upon
parallax measurements.
[1]
This is a
spectral type K1
giant star with about 1.25 M ☉ . The stellar envelope is slightly cooler than the Sun with an
effective temperature of 4,459 K, giving the star a light orange color. The
interferometry -measured
angular diameter of this star, after correcting for
limb darkening , is 3.93 ± 0.04
mas ,
[9] which, at its estimated distance, equates to a physical radius of about 16 times the
radius of the Sun .
[10]
τ Sagittarii is a suspected double star although no companion has been confirmed yet. A lower metal content (Fe to H ratio is 54% lower than the sun's) and a high
peculiar velocity (64 km/s, four times the local average) relative to the Sun suggest the star is a visitor from a different part of the Galaxy.
[11]
τ Sagittarii is a
red clump giant, a star with a similar mass to the sun which has exhausted its core hydrogen, passed through the
red giant branch , and started helium fusion in its core.
[12]
The Wow! signal
τ Sagittarii is the closest constellational star (a star that is part of the traditional outline of a constellation) to the origin of the 1977
Wow! signal .
[13]
Name and etymology
The star forms part of simple
asterisms :
γ Sgr , τ Sgr ,
δ Sgr ,
ε Sgr ,
ζ Sgr ,
λ Sgr ,
σ Sgr and
φ Sgr — the
Teapot .
[14]
φ Sgr , τ Sgr ,
ζ Sgr ,
χ Sgr (double) and
σ Sgr — the Returning Ostriches ; in Arabic Al Naʽām al Ṣādirah often transliterated as Namalsadirah (النعم السادرة).
[15]
ν Sgr , τ Sgr ,
ψ Sgr ,
ω Sgr ,
60 Sgr and
ζ Sgr , Al Udḥiyy — the Ostrich's Nest .
[15]
In the entirely separate
Chinese tradition — 斗 (Dǒu ), meaning
Dipper : τ Sgr,
φ Sgr ,
λ Sgr ,
μ Sgr ,
σ Sgr and
ζ Sgr . The star itself is 斗宿五 (Dǒu Xiù wǔ , English: the Dipper's fifth star ).
[17]
References
^
a
b
c
d
e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics , 474 (2): 653–664,
arXiv :
0708.1752 ,
Bibcode :
2007A&A...474..653V ,
doi :
10.1051/0004-6361:20078357 ,
S2CID
18759600
^
a
b
c
d Celis S., L. (October 1975), "Photoelectric photometry of late-type variable stars", Astronomy and Astrophysics Supplement Series , 22 : 9–17,
Bibcode :
1975A&AS...22....9C
^ Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample",
The Astronomical Journal , 132 (1): 161–170,
arXiv :
astro-ph/0603770 ,
Bibcode :
2006AJ....132..161G ,
doi :
10.1086/504637 ,
S2CID
119476992
^ Wilson, R. E. (1953). "General Catalogue of Stellar Radial Velocities". Carnegie Institute Washington D.C. Publication . Carnegie Institute of Washington D.C.
Bibcode :
1953GCRV..C......0W .
^
Brown, A. G. A. ; et al. (Gaia collaboration) (2021).
"Gaia Early Data Release 3: Summary of the contents and survey properties" .
Astronomy & Astrophysics . 649 : A1.
arXiv :
2012.01533 .
Bibcode :
2021A&A...649A...1G .
doi :
10.1051/0004-6361/202039657 .
S2CID
227254300 . (Erratum:
doi :
10.1051/0004-6361/202039657e ) .
Gaia EDR3 record for this source at
VizieR .
^ Cardini, D. (January 2005), "Mg II chromospheric radiative loss rates in cool active and quiet stars", Astronomy and Astrophysics , 430 : 303–311,
arXiv :
astro-ph/0409683 ,
Bibcode :
2005A&A...430..303C ,
doi :
10.1051/0004-6361:20041440 ,
S2CID
12136256 .
^ Reffert, Sabine; et al. (2015). "Precise radial velocities of giant stars. VII. Occurrence rate of giant extrasolar planets as a function of mass and metallicity". Astronomy & Astrophysics . 574 : A116.
arXiv :
1412.4634 .
Bibcode :
2015A&A...574A.116R .
doi :
10.1051/0004-6361/201322360 .
hdl :
10722/215277 .
S2CID
59334290 .
^ Hekker, S.; Meléndez, J. (2007). "Precise radial velocities of giant stars. III. Spectroscopic stellar parameters". Astronomy and Astrophysics . 475 (3): 1003.
arXiv :
0709.1145 .
Bibcode :
2007A&A...475.1003H .
doi :
10.1051/0004-6361:20078233 .
S2CID
10436552 .
^ Richichi, A.; et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics , 431 (2): 773–777,
Bibcode :
2005A&A...431..773R ,
doi :
10.1051/0004-6361:20042039
^ Lang, Kenneth R. (2006),
Astrophysical formulae , Astronomy and astrophysics library, vol. 1 (3rd ed.),
Birkhäuser ,
ISBN
3-540-29692-1 . The radius (R* ) is given by:
2
⋅
R
∗
=
(
10
−
3
⋅
37
⋅
3.93
)
AU
0.0046491
AU
/
R
⨀
≈
31.3
⋅
R
⨀
{\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(10^{-3}\cdot 37\cdot 3.93)\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 31.3\cdot R_{\bigodot }\end{aligned}}}
^
"The Teapot: A Guide to Deep Sky Objects in Sagittarius – Constellation Guide" . www.constellation-guide.com . Retrieved 2023-02-09 .
^ Alves, David R. (2000). "K-Band Calibration of the Red Clump Luminosity". The Astrophysical Journal . 539 (2): 732–741.
arXiv :
astro-ph/0003329 .
Bibcode :
2000ApJ...539..732A .
doi :
10.1086/309278 .
S2CID
16673121 .
^
"The world's biggest mysteries scientists still can't solve" . 2 September 2014. Archived from
the original on 8 November 2015. Retrieved 11 September 2015 .
^
"Teapot" . constellation-guide.com. Retrieved 2017-05-13 .
^
a
b
Allen, R. H. (1963).
Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p.
355 .
ISBN
0-486-21079-0 . Retrieved 2012-09-04 .
^
Jack W. Rhoads - Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars , Jet Propulsion Laboratory, California Institute of Technology; November 15, 1971
^ (in Chinese)
AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日